Last November or December, I finally discovered Malmo's Manifesto and the Summer of Malmo. So I planned on implementing double's this summer. But I forgot. Until last week. When another letsrun.com thread on two shorter runs v. one long run made me think that I could possibly up my mileage without further aggravating my butt or injuring something else by doing doubles. So I've started. Slowly. Short and slow. 4 miles in the morning and 5-7 miles in the afternoon. I'm starting with two doubles this week. Then 3 next week. If I'm still feeling good, I'll then do 3-4/week. What I will likely leave out for a while is a long run. Probably nothing over 8-10 miles (except the first half of the grafton notch loop which I'm doing next week - but that be more like a fast hike than a long run). I'm also leaving out intervals for a while. And hill repeats. I left out a tempo last week and I'm still considering leaving out a tempo this week. But next week I'll start tempos back up and maybe a couple of light progression runs.
Malmo pushing doubles is one example in a long list of runners who emphasize running alot. Wejo's Why I sucked in college is another example. I think my favorite example is from Bernd Heinrich in Why We Run: A Natural History, when he replaced all routine walking (through parking lots, down hallways, etc. etc.) with running when training for ultramarathons.